Henry can spend up to $400 on the cost of food, beverages, and invitations for the house party as the host of this event and this would not be considered a contribution to Cameron's campaign. Additionally, if Henry's spouse supports Cameron and would like to be involved, she too can spend an additional $400 on the party, for a total of $800.
The food and beverage exception in Public Act 10-1 does not apply to fundraising events. Since this is a fundraising event, Henry and his spouse should supply all the food and beverage, rather than having Wendy and Stella bring them.

Since this is not a fundraising event, Wendy can now make use of the exemption for food or beverage donated for consumption at a committee event that is not a fundraising affair to the extent the cumulative value of the food or beverage donated by the individual does not exceed $50. Stella cannot bring her steaks, however, since their value is over $50 and the entire $60 value would therefore be an impermissible in-kind contribution.
Note that in addition to the food brought by friends, Holly and her spouse may also spend up to $400 each on the cost of food, beverages, and invitations for the house party.

No, the exemption applies per individual, so each attendee may bring food or beverage valued at up to $50 to the party. This means that each attendee can bring food or beverages valued at $50.
The treasurer should keep a list of the individuals and what they brought for such events, as well any receipts they have for their purchases.

Yes, the $50 food and beverage exemption passed in Public Act 10-1 applies per event, so as long as Wendy's beverage donation does not exceed $50 at any given event, she can bring a bottle of wine to each non-fundraising event.

The above answers would be the same if Cameron were nonparticipating or a municipal candidate, except in cases where the attendees' food or beverage donation did not fit under the new exemption (either because the event was a fundraising event or because the value of the food or beverage donated at the event exceeded $50). Such donations would be permissible in-kind contributions to the non-participating or municipal candidate committees and would count toward that attendee's individual contribution limit.
Thus, for example, if Stella brought $60 worth of steaks to a fundraising event for a non-participating candidate, the entire $60 value would be considered an in-kind contribution. In other words, the exemption cannot be used to offset $50 of the value of the steaks with only $10 reported as an in-kind contribution.
If the candidate is in a slate committee rather than a candidate committee, the same answer holds true as the food and beverage exemption extends to both candidate committees and slate committees.

The treasurer will report the event in J1 of the SEEC Form 30 (or L1 of the SEEC Form 20 for municipal candidates), answering yes to whether the event was held at a personal residence.
Then, in J4 of the SEEC Form 30 (or L5 of the SEEC Form 20 in the case of municipal candidates), the treasurer will list all of the host's expenses for the party, listing the corresponding event number assigned in J1 (or L1 in the case of a municipal candidate). The treasurer will then itemize Wendy's donations in the same section, again listing the corresponding event number. If the candidate is nonparticipating or running for municipal office, then Stella's steaks would be reported as an in-kind contribution in Section K of the SEEC Form 30 (or Section M of the SEEC Form 20), listing the corresponding event number as well.